Enzymatic removal of the promutagenic alkylation lesion 06- methylguanine from DNA (a repair mechanism) can be exhibited in vitro in normal adult human tissues and bronchial epithelial cells or fibroblasts from culture. Successful cleavage demonstrates the catalytic activity of 06-alkylguanine-DNA alkyltransferase. Human tissues tested for alkyltransferase activity show highest levels in liver and decreasingly lower amounts in colon, esophagus, peripheral lung and brain. In some in vitro studies, repeated exposure to alkylating agents has induced higher levels in 06- methylguanine-DNA alkyltransferase activity, i.e., an adaptive response. Our previous studies indicate that human bronchial epithelial cells cannot be similarly induced; formaldehyde inhibits 06-methylguanine-DNA methyltransferase (06-MT) repair and potentiates mutagenicity of the alkylating agent, N-methyl-N- nitrosourea, in normal human fibroblasts. These findings have important implications in carcinogenesis caused by low doses of N- nitrosamines. To resolve the indications of these results we are studying: a) the in vitro effects of cigarette smoke condensate (CSC), catechol and smoke "conditioned" media on the activity of 06-MT and uracil-DNA glycosylase (UDG) in cultured human bronchial epithelial cells (NHBE), HuT 292 cells and BEAS-12 cells; and b) the effects of the polycyclic aromatic hydrocarbons (PAH) in smokers and nonsmokers on the activity of these DNA repair enzymes measured in alveolar macrophages and peripheral blood lymphocytes. Preliminary results show that a) neutral CSC induces 12-0- tetradecanoylphorbol-13-acetate (TPA)-like activity in NHBE cells; and b) interindividual and intraindividual activities in blood cells vary 100-fold and 6-fold, respectively, while, compared to nonsmokers, macrophages of smokers contain significantly higher levels of UDG activity, the levels of which appear related to the detectibility of polycyclic aromatic hydrocarbon-DNA adducts in both cell types studied. The levels of both UDG and 06-MT were related to smoking in macrophages with PAH-DNA adducts.